JCMmode: An Adaptive Finite Element Solver for the Computation of Leaky Modes

We present our simulation tool JCMmode for calculating propagating modes of an optical waveguide. As ansatz functions we use higher order, vectorial elements (Nedelec elements, edge elements). Further we construct transparent boundary conditions to deal with leaky modes even for problems with inhomogeneous exterior domains as for integrated hollow core Arrow waveguides. We have implemented an error estimator which steers the adaptive mesh refinement. This allows the precise computation of singularities near the metal's corner of a Plasmon-Polariton waveguide even for irregular shaped metal films on a standard personal computer.Comment: 11 page

Mid-infrared observations of the SGR 1900+14 error box

We report on mid-infrared observations of the compact stellar cluster located in the proximity of SGR 1900+14, and the radio/X-ray position of this soft-gamma repeater. Observations were performed in May and June of 2001 when the bursting source was in an active state. At the known radio and X-ray position of the SGR we did not detect transient mid-IR activity, although the observations were performed only hours before and after an outburst in the high-energy band.Comment: 4 pages, 3 figures, to appear in "Gamma-Ray Burst and Afterglow Astronomy 2001", Woods Hole; 5-9 Nov, 200

In Situ Diffuse Reflectance IR Spectroscopic Investigation of n-Butane Isomerization on Promoted Sulfated Zirconia Catalysts

Introduction Sulfated zirconia (SZ) is an attractive catalyst for low temperature butane isomerization [1]. Its activity can be improved by 1–2 orders of magnitude through addition of promoters such as iron or manganese in cationic form [2,3]. The state of these promoters has been characterized, and depending on the method of preparation, a major fraction is found to form a solid solution with zirconia [4]. It has been proposed that promoters facilitate reaction initiation via oxidative dehydrogenation to butenes, which may be converted into the reaction carriers, viz. carbenium ions. Only indirect evidence such as better activity after activation in oxidizing than in inert atmosphere has been presented [5]. Reaction profiles recorded under moderate reaction conditions (e.g. 323 K, 1 kPa n-butane) show an induction period and zero conversion in the extrapolation to zero time on stream. Either the catalyst becomes active only in the feed, or intermediates accumulate on the surface. We have focused on manganese as a promoter and have used in situ diffuse reflectance IR spectroscopy (DRIFTS) to reveal the effects of activation or regeneration in inert gas or O2, and to monitor the events during the induction period. References 1. Hino, M., Arata, K., J. Am. Chem. Soc. 101, 6439 (1979). 2. Hsu, C.-Y., Heimbuch, C.R., Armes, C.T., Gates, B.C., Chem. Commun. 1645 (1992). 3. Lange, F.C., Cheung, T.-K., Gates, B.C., Catal. Lett. 41, 95 (1996). 4. Jentoft, F.C., Hahn, A., Kröhnert, J., Lorenz, G., Jentoft, R.E., Ressler, T., Wild, U., Schlögl, R., J. Catal. 224, 124 (2004). 5. Wan, K.T., Khouw, C.B., Davis, M.E., J. Catal. 158, 311 (1996)

On the Origin of the Dark Gamma-Ray Bursts

The origin of dark bursts - i.e. that have no observed afterglows in X-ray, optical/NIR and radio ranges - is unclear yet. Different possibilities - instrumental biases, very high redshifts, extinction in the host galaxies - are discussed and shown to be important. On the other hand, the dark bursts should not form a new subgroup of long gamma-ray bursts themselves.Comment: published in Nuovo Ciment

The Balance Between Reactivity and Stability of Modified Oxide Surfaces Illustrated by the Behavior of Sulfated Zirconia Catalysts

The stability of a series of sulfated zirconia catalysts, promoted with up to 2 wt% iron or manganese, in their calcined state was investigated. Phase composition, nature of surface sulfate species, degree of hydroxylation, and butane isomerization activity changed during aging over months in various atmospheres and during milling. The metastability of small oxide particles is discussed, including literature data on alumina, titania and other oxides. Catalytically active fractions of a material easily transition into more stable, less active forms

Numerical Investigation of Light Scattering off Split-Ring Resonators

Recently, split ring-resonators (SRR's) have been realized experimentally in the near infrared (NIR) and optical regime. In this contribution we numerically investigate light propagation through an array of metallic SRR's in the NIR and optical regime and compare our results to experimental results. We find numerical solutions to the time-harmonic Maxwell's equations by using advanced finite-element-methods (FEM). The geometry of the problem is discretized with unstructured tetrahedral meshes. Higher order, vectorial elements (edge elements) are used as ansatz functions. Transparent boundary conditions and periodic boundary conditions are implemented, which allow to treat light scattering problems off periodic structures. This simulation tool enables us to obtain transmission and reflection spectra of plane waves which are incident onto the SRR array under arbitrary angles of incidence, with arbitrary polarization, and with arbitrary wavelength-dependencies of the permittivity tensor. We compare the computed spectra to experimental results and investigate resonances of the system.Comment: 9 pages, 8 figures (see original publication for images with a better resolution